The present invention relates to a method and to devices and subnetworks for the protection of STM-N/OC-n clear channel connections.
STM-n/OC-n clear channel interconnection is the ability of a network or network devices to interconnect an STM-n/OC-n signal as it is without processing in the case of STM-n signals, RSOH (Regeneration Section Overhead) bytes and MSOH (Multiplex Section Overhead) as defined in ITU-T specifications G.783 and G.707 (November 1995) or, in case of OC-n signals, of the Section and Line Overheads as defined in Bellcore GR-253.
Assuming connection with an STM-n/OC-n signal of two network elements (NE A and NE C) passing through a third element NE B capable of realizing only VC-n/STS-n (not clear channel) connections, NE B terminates the received STM-n/OC-n A and generates a new signal (STM-n/OC-n B) towards NE C with the same VC-n/STS-n within but with different RS/Section OH and MS/line OH.
Even if no regeneration, grooming and consolidation operations are required on an STM-n signal traversing a conventional SDH/SONET node, i.e. a Digital Cross Connect—DXC—or an Add/Drop Multiplexer—ADM—, termination of the RS/Section Overhead and possibly termination of the MS/Line Overhead with resulting interconnection at the VC-n/STS-n level are carried out nevertheless.
If the same connection is made over an NE B able to provide clear channel connections (see FIG. 2), then the STM-n/OC-n A signal generated by NE A will reach NE C without any modification.
In addition, some of the bytes of RS/Section OH and MS/line OH could be used for end-to-end transportation of data defined in standards (for example the K1 and K2 bytes could transport the switching protocol for automatic protection, the Di bytes could transport data communication channels) or proprietary data (for example “Media Dependent Bytes”, “Byte Reserved for National Use”, “Spare Byte”, etc.).
Processing of the RS/Section and MS/Line overhead bytes even if there is no need of regeneration, grooming or consolidation operations could cause premature termination of these data. The STM-n/OC-n clear channel interconnection allows this type of data to pass through the nodes where no intrusive process is required.
But, at the present time, no protection system is provided for STM-N/OC-n clear channel connections even though a sort of protection is required for this type of switched entity to protect the transmission of the STM-n/OC-n from the source point to the destination point or even to protect any subnetwork connection of the STM-n/OC-n route.